Abstract

An undescribed apical chlorosis caused severe losses in seedlings of Tagetes erecta and T. patula types in Sydney, Brisbane and Melbourne in 1976. Bacterial leaf spots without chlorotic haloes invariably accompanied the disease. The same bacterium was isolated from leaf lesions and chlorotic tissue and produced leaf spots and chlorosis on marigold, zinnia and sunflower with spray inoculation. Leaf spots did not develop on T. signata. Apical chlorosis developed on a diverse range of plants following wound inoculation. The pathogen was shown to be seed-borne. The pathogen was identified as Pseudomonas tagetis, cultural and biochemical characteristics described, and a neotype culture proposed. An exotoxin was produced in vitro which caused apical chlorosis in Zinnia elegans and T. patula.